How sudo sets the PATH value when secure_path is not defined

Last Modified: Thu, 16 Apr 2015 20:16:12 +0000 ; Created: Thu, 16 Apr 2015 20:14:50 +0000

Ran across an interesting technical detail while working on a PATH configuration problem in my /etc/profile. When no PATH is defined (such as when you do sudo -i) the sudo command will inject a standard one that is compiled into its code. This applies when you do not have a secure_path option either in your config or built-in as a compile option at build time.

This was important because when using bash and before your /etc/profile configures your PATH variable there will be an already existing value setup by the sudo -i command (or sudo -s env). This mostly affected me due to some invocations creating a PATH with two colons (::) in it which was a security issue for root since that implies the current working directory is in root's PATH.

Testing was done on a Red Hat 6. Sudo version 1.8.6p3 with 1.8.6p3-12.el6.

Regular (non-root) user logged in via ssh:

Before /etc/profile the sshd process sets PATH=/usr/local/bin:/bin:/usr/bin (or whatever value your OpenSSH was configured and compiled to use).

sudo -i OR sudo -s env

Before /etc/profile the sudo process sets PATH=/usr/bin:/bin:/usr/sbin:/sbin

Sudo source code that shows the value it uses

sudo-1.8.6p3.tar/sudo-1.8.6p3/sudo-1.8.6p3/ _PATH_STDPATH         "/usr/bin:/bin:/usr/sbin:/sbin"

    /* Provide default values for $TERM and $PATH if they are not set. */
    if (!ISSET(didvar, DID_TERM))
	sudo_putenv("TERM=unknown", false, false);
    if (!ISSET(didvar, DID_PATH))
	sudo_setenv2("PATH", _PATH_STDPATH, false, true);